Radiation screen for rotary kilns



July 13, 1937. A. w. HEYMAN RADIATION SCREEN FOR ROTARY KILNS FiledApril 9, `1936 zzlezzzrl offzr/J/Wm:

r @MW l l Patented July 13, 1937 UNITED lsTATEsD PATENT OFFICE RADIATIONSCREEN FOR ROTARY KILNS Arthr W. Heyman, Allentown, Pa.

Application April 9, 1936, Serial No. 73,539

1 Claim.

The invention relates to rotary cement kilns andhas particular referenceto improvements adapting the kilns foruse in melting or entirely fusingthe product, as for example, in the manufacture of aluminate cementwhich is fused 'instead of merely sintered as in the case of Portlandcement. v

In the progress `of raw material through the kiln it changes from thegranular or pulverulent p condition, which it usually possesses when itentersthekiln, to the molten 'condition which it possesses when itleaves. In the kiln the material passes through an intermediate state inwhich it is semi-molten and possesses viscous,

gummy or sticky characteristics. In this stage it readily adheres to *he'lining of the kiln and' ing zone but requires the'radiant heat of thevflame-plume itself. Y

In order-to prevent or reduce the formation of rings the inventionprovides a radiation screen' 30 of such construction and so located asto confine the highest temperatures to the melting zone of ular orpulverulent material becomes gummy or sticky.

Another object is to provide a series of openings or tap holes in thekiln in back of the radiation screen of said kiln through which openingsthe pulverulent material dammed up by the 40 screen may be removed fromthe kiln.

With these and various other objects in view the invention may consistof certain novel features of construction and operation as will be morefully described and particularly pointed out 45 in the specification,drawing and claim appended hereto.

In the drawing which illustrates an embodiment of the invention andwherein like reference characters are used to designate like parts- 50Figure I is a view mainly in longitudinal section showing a rotary kilnembodying the features of the invention;

Figure 2 is a transverse sectional view through the radiation screentaken substantially alon -55 line 2--2 l l Figure 3 is a fragmentarylongitudinal sectional view of a kiln equipped with a modified form ofradiation screen; and

Figure 4 is a transverse sectional view taken substantially along line4-4 of Figure 3. 5

The kiln illustrated in Figure 1`is indicatedin its entirety by numerall0 and consists of the usual cylindrical steel shell Il lined withrefractory lining I2. The kiln is supported at intervals throughout itslength by supports i3 l0` which are provided with rollers I4 engagingthe annular metal tire I 5. The kiln is accordingly mounted for rotationand is disposed at a slight inclination to the horizontal. The low endof the vkiln or the melting zone thereof is provided with 15 a conicalignition hood I6 which consists of an outer conical steel shell l1 linedwith refractory lining l8.- 'Ihe'ignition hood is provided with an axial'opening 20 for admitting the nozzle 22 of the burner pipewhich conveysthe fuel to be burned and which produces within the melting zone of thekiln the flame-plume 23. The opening 20 is partially closed, by a plate24 spaced the proper distance from the end of the kiln in order to allowvarying amounts of secondary air Y to enter.

At a point beyond thev ame-plumevthe kiln is provided with aradiationscreen 25 which'may be constructed in a number of ways but it ispreferredrto make the screen of a fire resistant concrete composed ofsuitable refractory aggregate bound together with Lumnite an aluminatecement. The screen is in eifect an annular ring within the kiln andforms `a restricted passage 26 through which passes the gases from 35the melting zone and the material from the preheating or low temperaturezone of the kiln. Also the screen by reason of the inclination of thekiln dams up a considerable quantity, indicated by numeral 21, of thegranular or pulverulent material fed to the kiln. The radiation screenis water cooled by means of tubes 28 which extend from the periphery ofthe kiln well into the radiation screen. The tubes and their radialarrangement are more particularly 'disclosed in Figure 15 2. A watersupply pipe 30 is located over the kiln directly above the opening ofthe tubes 28 for supplying cooling water thereto, which is dischargedfrom the tubes when they reach their lowermost position.

Another form of radiation screen 3| is shown in Figure 3. In this formthe screen has a rounded nose dening the restricted passage 32. Thismodified screen is cooled by theV annular trough 33 formed in the screenand which ex- 55 tends from the periphery of the kiln well into the noseof the screen. Metal partitions 34 are inserted at intervals throughoutthe circular extent of the trough and are accordingly radially disposedas shown in Figure 4.

'I'he preferred location of the radiation screen longitudinally of thekiln is dependent on several factors, the most important of which is thelength of the name-plume, which is of course dependent on variousfactors including the amount of fuel consumed per unit of time and inthe case of coal the amount of primary air used and the amount ofvolatile matter in the coal. In general, the best location is at orslightly beyond the tip of the flame-plume. The depth of the radiationscreen, or conversely, the diameter of the restricted passageway formedthereby, depends on various operating factors, but the best results havebeen secured by having the radiation screen occupy approximatelythree-fourths of the area of the kiln at that point, thus allowing aboutone-fourth for the passage of the material to be melted and thecounter-current passage of the gases leaving the burning or meltingzone.

The invention is not limited to the location, size nor method ofconstruction of the radiation screen. These factors may varyconsiderably Without seriously affecting the efficiency of the apparatusif the construction is such as to accomplish the main object which is toshield the granular material being preheated or calcined in the upperpart of the kiln from the radiant heat of the flame plume of the meltingzone. dentally, the construction of the invention increases theeflciency of the kiln by causing the high temperature heat to bereflected back into the burning zone instead of allowing it to bedissipated into the preheating or calcining zone. where low temperatureheat only is required.

Under certain conditions the material being treated may form a ring evenwhen the kiln is provided with a radiation screen. In such cases thering usually forms in front of the radiation screen, that is, toward thefiring end of the kiln. At the same time the granular or pulverulentmaterial 21 will be dammed up back of the radiation screen. The removalof this ring is ordinarily accomplished by burning or melting it out,which requires that the feeding of the material be discontinued and thename-plume is then controlled so that the hottest part of theflame-plume is arranged to be in as close proximity as possible to thering. The increased temperature causes Incithe ring material to melt andiiow to the discharge end of the kiln. The material 21 dammed up in backof the radiation screen will not be melted but is only brought to thegummy or sticky condition, and if operation of the kiln were to beresumed another ring back of the radiation screen or back of Said firstring would r be formed.

To prevent the formation of repeating rings the kiln of the invention isprovided with a tap hole or a series of tap holes 36 located directlyback of the radiation screen at which point the repeating ringsgenerally occur. Plates 31 are provided for closing said tap holes 36,the wedges 38 effectively holding the plates in position. By means ofthese openings it is possible to remove substantially all of thegranular or pulverulent material from in back of the screen, thuspreventing the formation of additional rings. The material is removedfrom the tap holes 36 and the ring is melted out as above described. Theoperation of the kiln can now be resumed with the normal length offlame-plume and the material removed from the tap holes is fed back intothe kiln.

The invention is not to be limited to or by details of construction ofthe particular embodiment thereof illustrated by the drawing, as variousother forms of the device will of course be apparent to those skilled inthe art without departing from the spirit of the invention or the scopeof the claim.

What is claimed is:

In a rotary kiln comprising a cylindrical body portion, means supportingsaid body portion for rotation and at a slight inclination to thehorizontal whereby one end of the kiln is lower than the other end, anignition hood fixed to the body portion of the lower end thereof whichcomprises the discharge end of the kiln, Said hood having an axialopening for admitting the nozzle of a fuel burner, a radiation screenwithin the body portion dividing the kiln into a melting zone and a lowtemperature zone, said melting zone comprising the portion of the kilnfrom said radiation screen to the ignition hood, means extending fromthe periphery of the kiln into said radiation screen for cooling thesame, said kiln having openings therein on the upper side of the'radiation screen providing access to the low temperature zone, and meansfor closing said openings.

ARTHUR W. HEYMAN.

